Improved USB Microscope Adapter for Modular Stand

This is an improved adapter for those generic cheap 50x to 1000x / 1600x USB microscopes, compatible with [Chrlee](https://www.thingiverse.com/Chrlee)'s excellent [modular stand for electronic microscopes](https://www.thingiverse.com/thing:2780973). The author provided a [similar adapter](https://www.thingiverse.com/thing:2783956), but I found it to be extremely loose to the point that breathing on the cable could cause the scope to wobble. Mine is significantly tighter and more accurately fitted.

There are two little nubs on each end of the holder similar to the microscope's original stand. These provide additional clamping force, but can be easily snipped off for a less aggressive fit if desired.